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The formal 1,3-cycloaddition of 2-diazocyclohexane-1,3-diones 1a–1d to acyclic and cyclic enol ethers in the presence of RhII-catalysts to afford dihydrofurans has been investigated. Reaction with a cis/trans mixture of 1-ethoxyprop-1-ene (13a) yielded the dihydrofuran 14a with a cis/trans ratio of 85 : 15, while that with (Z)-1-ethoxy-3,3,3-trifluoroprop-1-ene (13b) gave the cis-product 14b exclusively. The stereochemical outcome of the reaction is consistent with a concerted rather than stepwise mechanism for cycloaddition. The asymmetric cycloaddition of 2-diazocyclohexane-1,3-dione (1a) or 2-diazodimedone (=2-diazo-5,5-dimethylcyclohexane-1,3-dione; 1b) to furan and dihydrofuran was investigated with a representative selection of chiral, nonracemic RhII catalysts, but no significant enantioselectivity was observed, and the reported enantioselective cycloadditions of these diazo compounds could not be reproduced. The absence of enantioselectivity in the cycloadditions of 2-diazocyclohexane-1,3-diones is tentatively explained in terms of the Hammond postulate. The transition state for the cycloaddition occurs early on the reaction coordinate owing to the high reactivity of the intermediate metallocarbene. An early transition state is associated with low selectivity. In contrast, the transition state for transfer of stabilized metallocarbenes occurs later, and the reactions exhibit higher selectivity.

The Cu‐catalyzed intramolecular CH insertion of phenyliodonium ylide 1b was investigated at 0° in the presence of several chiral ligands. Enantioselectivities varied in the range 38–72%, and were higher than those resulting from reaction of the diazo compound 1c at 65°. The intramolecular insertion of the enantiomerically pure methyl diazoacetate (R)‐20 and of the corresponding phenyliodonium ylide (R)‐21 proceeded to (R)‐23 with retention of configuration with [Cu(hfa)₂] (hfa=hexafluoroacetylacetone=1,1,1,5,5,5‐hexafluoropentane‐2,4‐dione) and [Rh₂(OAc)₄]. These results are consistent with a carbenoid mechanism for the Cu‐catalyzed insertion with phenyliodonium ylides. However, the insertion of the perfluorosulfonated phenyliodonium ylide (R)‐29 afforded with [Cu(hfa)₂] as well as with [Rh₂(OAc)₄] the cyclopentanone derivative 30 as a cis/trans mixture with only 56–67% enantiomeric excess.

The enantioselectivity of the copper-catalyzed intramolecular cyclopropanation of allyl diazomalonates and the corresponding phenyliodonium ylides was investigated with a series of chiral, non-racemic ligands. The reaction of 6b in the presence of the bis[dihydrooxazole] ligand Xa in refluxing 1,2-dichloroethane proceeded to 8b with an enantiomer excess (ee) of up to 72% under optimized conditions. In contrast, 8b resulting from reaction of ylide 7b with the same ligand, but in CH2Cl2 at 0°, had an ee of only 30%. With other ligands, diazomalonate 6b reacted with a lower enantioselectivity than ylide 7b, however. The intramolecular cyclopropanation of the acetoacetate-derived phenyliodonium ylide 15b afforded 16b with 68% ee with ligand Xa, but the corresponding diazo compound was unreactive when exposed to chiral copper catalysts. The observation of asymmetric induction in the Cu-catalyzed reactions of the ylides 7 and 15 is consistent with a carbenoid mechanism; however, the discrepancy of the enantioselectivities observed between diazomalonate 6b and ylide 7b suggests a competing unselective pathway for cyclopropanation outside of the coordination sphere of copper.

The cyclohexene-derived aziridine 7-tosyl-7-azabicyclo[4.1.0]heptane (1) reacts with Grignard reagents in the presence of chiral nonracemic Cu-catalysts to afford sulfonamides 3a – e (Scheme 3) in up to 91% ee under optimized conditions (Table 2). No activation of the aziridine by Lewis acids is required. The reaction may be extended to other bicyclic N-sulfonylated aziridines, but aziridines derived from acyclic olefins, cyclooctene, and trinorbornene are unreactive under standard conditions (Scheme 5). Exposure of 1 to s-BuLi in the presence of (−)-sparteine (2.8 equiv.) affords the allylic sulfonamide 31 in 35% yield and 39% ee (Scheme 6). Under the same conditions, the aziridines 33 and 35 yield products 34 and 36 derived from intramolecular carbenoid insertion with 75 and 43% ee, respectively.

The stereochemical course of the thermal 2-aza-Cope rearrangement of the optically pure acyl azide (−)-(1S)-5 was investigated by determination of the absolute configuration of the rearrangement product (1R,8S)-9. The reaction proceeds by a sequence of stereospecific steps from 5 to an equilibrating mixture of exo- and endo-isocyanates 6 and 7. The endo-isomer 7 undergoes Cope rearrangement to the putative intermediate 8, which is trapped and characterized as the adduct 9b of butan-1-ol. The absolute configuration of 9b was determined by its reduction to the amide 20, and determination of the X-ray structure of the N-camphanoylamide 21 derived from camphanic acid of known absolute configuration.

Treatment of (aR)‐[1,1′binaphthalene]‐8,8′‐diol ((−)‐1) with hexamethylphosphorous triamide afforded the N,N‐dimethylphosphoramidite (−)‐3 (Scheme 1). The synthesis of the analogous N,N‐diisopropylphosphoramidite 4 failed, however, and afforded the acyclic phosphonamidate (−)‐5. The application of the cyclic phosphoramidite (−)‐3 towards asymmetric catalysis was investigated. The borane reduction of acetophenone (6) to (R)‐1‐phenylethanol (7) in the presence of (−)‐3 proceeded with 96% ee (Scheme 2). The use of (−)‐3 as ligand in several Cu‐catalyzed addition and substitution reactions resulted in enantioselectivities ranging from 0 to 50% (Schemes 3 and 4).

Olefins undergo cyclopropanation with diphenylsulfonium (ethoxycarbonyl)methylide (=diphenylsulfonium 2‐ethoxy‐2‐oxoethylide; 3a) in the presence of chiral CuI or RhII catalysts. trans/cis Ratios and ee's of the cyclopropanes 6 obtained with this ylide in the presence of a chiral CuI catalyst 7 are identical with those obtained with ethyl diazoacetate (4). In the case of catalysis with RhII, the trans/cis ratios of the cyclopropanes as well as the enantioselectivity change slightly upon going from the ylide 3a to diazoacetate 4.

The optically active cyclopropanecarbonyl azide 6 (ee 90%) was synthesized from the known cyclopropanecarboxylate 4. Upon heating in refluxing benzene, 6 rearranged to the dihydroazepinone 9 (ee 65%) via the isocyanate 7 and the enamide 8. In contrast, the dimethyl‐substituted cyclopropanecarbonyl azide 20 rearranged to the isocyanate 21, but decomposed at higher temperatures rather than to undergo Cope rearrangement to 22. The results are consistent with a mechanism involving a boat‐like endo‐transition state 11 for the rearrangement, which may not be reached with the dimethyl derivative 21 for steric reasons. The origin of change in enantiomer composition, upon going from 6 to 9, is at present unknown.

The cyclopropenation of diethoxypropyne (1) with methyl diazoacetate in the presence of [Rh₂{(2S)‐mepy}₄] (mepy=methyl 5‐oxopyrrolidine‐2‐carboxylate) proceeds with >95% ee. The resulting cyclopropenecarboxylate 2 underwent stereoselective hydrogenation to the cis‐cyclopropane 3. Hydrolysis of the acetal function of 3 liberated the formyl cyclopropenecarboxylate 4, which was transformed by Wittig reaction with the phosphonate 5 to afford dehydroamino acid 6 as a mixture of (Z)‐ and (E)‐isomers in various proportions. The (Z)‐isomer 6a was hydrolyzed, and the structure and the absolute configuration of the (Z)‐dicarboxylic acid 7a were established by X‐ray crystallography. The cis‐divinylcyclopropane 11 (ee>95%), in turn, was synthesized from 4 via Wittig reaction to afford 8, which was transformed to the aldehyde 10 and subjected to a second Wittig reaction. Thermolysis of 11 afforded (+)‐dictyopterene C′ (12) in quantitative yield.

The [Rh₂(OAc)₄]‐catalyzed decomposition of {[(4‐nitrophenyl)sulfonyl]imino}phenyl‐λ³‐iodane (NsN=IPh) resulted in formal insertions into CH bonds, activated by phenyl or vinyl groups, or by O‐substituents. Scope and limitations of the reaction were investigated. Yields of up to 84% were achieved in the most favorable cases. Yields were enhanced by electron‐releasing substituents and decreased by steric hindrance. Aziridination competed with allylic insertion with olefinic substrates. The insertion reaction proceeded with retention of configuration. With chiral RhII catalysts, a modest asymmetric induction was observed. A mechanism involving direct insertion by a Rh‐complexed nitrene into the CH bond is proposed.

The [Rh2(OAc)4]-catalyzed addition of methyl diazoacetate to N-benzylideneaniline (1a) afforded the imine cis-2 in 35% yield. Under catalysis by chiral RhII catalysts, however, only racemic 1a was produced, and the yield was low. In the presence of dimethyl maleate, aziridine formation was suppressed, and an intermediate ylide 6 was trapped as cycloadduct 7. No aziridines were obtained, however, from 1b, 1c, and 3. The iminium salt 8 reacted with (trimethylsilyl)diazomethane in the absence of [Rh2(OAc)4] via dipolar cycloaddition followed by extrusion of N2 to 10.

The intermediacy of metallocarbenes in decomposition reactions of iodonium ylides with [Rh2(OAc)4] was established by comparison with reactions of the corresponding diazo compounds. The sensitivity of the RhII-catalyzed intermolecular cyclopropane formation from substituted styrenes and bis(methoxycarbonyl)(phenyliodono)methanide (1a) or dimethyl diazomalonate (1b) is identical. The Hammett plot (with σ+) has a slope of −0.47. Iodonium ylides and diazo compounds afford the same products in [Rh2(OAc)4]-catalyzed cyclopropane formations, cycloadditions, and intramolecular CH insertions, and exhibit the identical selectivity in intramolecular competitions for cyclopropane formation and insertion. The intramolecular CH insertion of the ylide 20c, when carried out in the presence of a chiral catalyst ([Rh2{(−)-(S)-ptpa}4]), results in formation of 21a having an ee of 67%, identical to the ee obtained with the diazo compound 20b.

The Rh¹¹‐catalyzed carbenoid addition of diazoacetates to olefins was investigated with [Rh₂{(4S)‐phox}₄] (1;phox = tetrakis[(4S)‐tetrahydro‐4‐phenyloxazol‐2‐one]), [Rh₂{(2S)‐mepy}₄] (2; mepy = tetrakis[methyl (2S)‐tetrahydro‐5‐oxopyrrole‐2‐carboxylate]), and [Rh₂(OAc)₄] (3). While catalysis with 2 and 3 afford preferentially trans‐cyclopropanecarboxylates, the cis‐isomers are the major products with 1. In general, the enantioselectivities achieved with 1 and 2 are comparable. Additions catalyzed by 1 are strongly sensitive to steric effects. Highly substituted olefins afford cyclopropanes in only poor yield. The preferential cis‐selectivity observed in reactions catalyzed by 1 is attributed to dominant interactions between the ligand of the catalyst and the substituents of both olefin and diazoacetate, which overrule the steric interactions between olefin and diazoacetate in the transition state for carbene transfer.

The course of the thermocatalytic rearrangement of cycloprop-2-ene-1-carboxylates in the presence of dirhodium(II) tetrakis(perfluorobutyrate) ([Rh2(pfb)4]) was investigated by varying the substituents of the cyclopropene ring. Product composition is markedly influenced by the number, nature, and position of the substituents, which determine the regio- and stereoselectivity of the cyclopropene-ring cleavage. A mechanism is proposed in which attack of the electrophilic RhII species is concerted with disrotatory ring opening of the incipient cyclopropyl cation and affords a metal-complexed vinylcarbene. The chemoselectivity of the latter is consistent with that of other carbenes generated in the presence of [Rh2(pfb)4].

The heterocyclic cycloprop[f]indene 19 was synthesized via cycloaddition of diene 10 to the cyclopropene 11a and subsequent base-induced aromatization. While 19 is isolable, although very short-lived, the oxa analogue 18 decomposed under the conditions required for its preparation. The difluoro derivatives 14 and 15, in which the heterocyclic moiety is saturated, are accessible by the cycloaddition approach, but the corresponding dichlorides are again not isolable. Cycloprop[f]indenes carrying substituents at C(4) have been obtained via cycloaddition of 22b to 1-bromo-2-chlorocyclopropene. The key step of the sequence is a double Curtius degradation of the cycloadduct 23b to the ketone 27a. While aromatization of the alcohol 27b provided the cycloprop[f]indenol 28b, the reaction failed with 27a. Attempts to convert 28b to 1,3-dihydrocycloprop[f]indene (25) via the methanesulfonate 28d failed.

The synthesis of 4,5-dihydro-1H,3H-cycloprop[f]inden-4-ol (1) and diethyl 4,5-dihydro-1H,3H-cycloprop[f]-indene-4,4-dicarboxylate (26) starting from diene 4 is described. The cyclopentene ring is constructed by condensation of diethyl malonate to the dibromide 21. The key-step in the synthesis of 1 consists in a twofold Curtius degradation of 22, with subsequent reduction of the carbonyl group and aromatization. The skeleton of the isomer 31 is synthesized via cycloaddition of butadiene to cyclopent-4-ene-1,3-dione (7) and addition of dichlorocarbene to the adduct 27 after ketalisation. The attempted synthesis of dihydrocycloprop[f]indene (2) by base-induced elimination of several appropriately substituted precursors failed.

The decomposition of cyclohexyl diazoacetate (5a) in the presence of the chiral [Rh2{(2S)-mepy}4] catalyst leads to a 3:1 cis/trans mixture of bicyclic lactone 6a with an enantiomeric excess of 95–97% (cis) and 90% (trans). The conformationally rigid tert-butyl derivatives 5b and 5c afford, in the presence of the same catalyst, 6b and 6c, respectively, via insertion into the equatorial C-H bonds exclusively, with ee's of ca. 95%. A remarkable degree of induction (92–95%) results in the lactone 6g upon decomposition of 1-isopropyl-2-methylpropyl diazoacetate (5g). The diazoacetates derived from 1-methylcyclohexanol, cyclopentanol and 1-methylcyclopentanol (5d–f) afford under similar conditions insertion products with higher diastereoselectivity, but significantly lower enantioselectivity. Other dirhodium catalysts are less efficient.

The synthesis and X-ray structure of the binuclear complex tetrakis[(4S)-4-phenyloxazolidin-2-one]-dirhodium(II) ([Rh2{(4S)-phox}4]) are reported. Structure-selectivity comparisons are made for typical metal carbene transformations, such as inter- and intramolecular cyclopropane formation, intermolecular cyclopropene formation and intramolecular C–H insertions of diazoacetates and diazoacetamides. The enantioselectivity achieved in the [Rh2{(4S)-phox}4]-catalyzed reactions is intermediate between that of [Rh2{(5S)-mepy}4] and [Rh2{(4R)-bnox}4], which were described previously (mepy = methyl 5-oxopyrrolidine-2-carboxylate; bnox = 4-benzyloxazolidin-2-one). In contrast to other catalyzed intermolecular cyclopropane formations, those using [Rh2{(4S)-phox}4] result preferentially in formation of the cis-cyclopropane.

By unambiguous methods, (Z)- and (E)-2, 3-dimethyl(1, 1, 1, 4, 4, 4-2H6)but-2-enes (3) were synthesized and transformed to the epoxides 4 with 3-chloroperbenzoic acids. Both the isotopomeric olefins and the epoxides are detected separately by 1H-NMR at 400 MHz. Epoxidation of (Z)-3 with [RhICl(PPh3)3]/cumene hydroperoxide resulted in a 1: 1 mixture of (Z)- and (E)-4, while reaction of (Z)-3 with [FeIII(tpp)]Cl/PhIO gave only (Z)-4 (tpp = tetraphenylporphyrin).

Force-field parameters have been developed for the molecular-mechanics calculation of tertiary carbenium ions with tricyclane structure, for tertiary cyclobutyl and cubyl cations. The cyclobutyl parameters are also applicable to tertiary 7-norbornyl cations. Satisfactory plots are obtained for correlation of the rates of solvolysis with the differences in steric energies between carbenium ions and the corresponding bromides.

The stereo and face selectivities of the cycloaddition of 1,2,3-trichloro-3-fluorocyclopropene (1a) with acyclic dienes and furans has been re-investigated by X-ray determination and correlation of 19F-NMR data. The isolated adducts of dienes exclusively have exo-configuration, and exo-Configuration predominates with furans. The Cl substituents of the resulting cyclopropane ring are cis-oriented. The face selectivity of the reaction with both types of substrates is attributed to electrostatic interactions between the F and the bridgehead Cl substituents, which destabilize the F-cis-transition state (13 (F-cis)) over 13 (F-trans).

In presence of crown ether, 2-alkoxy-1,1-dichlorocyclopropanes react with t-BuOK/THF preferentially via ring opening to 2-chloroalk-2-en-1-ones and alkynones or to chlorocyclopropenes. The latter may be intercepted with 1,3-diphenylisobenzofuran, but in the absence of trapping agent, the rearrangement to vinylcarbenes does not occur.

1H-Cyclopropa[g]quinoline (3-aza-lH-cyclopropa[b]naphthalene; 17) was synthesized via interception of the heterocyclic ortho -quinodimethane 15 with l-bromo-2-chlorocyclopropene, followed by aromatization of the adduct 16 with t-BuOK.

Reaction of the carbanions derived from chloromethyl phenyl sulfone or 1 -chloroethyl phenyl sulfone with the cationic [Fe(arene)Cp] complexes 8 or 9 produced isolable c-adducts 10-12. Attempted base induced elimination of the s̀-adducts, which would have led to products of vicarious nucleophilic substitution (VNS reaction), failed. Similarly, no VNS products were obtained, when the (arene)tricarbonylchromium complexes 4 were reacted with the anion of chloromethyl phenyl sulfone.

1H-Cyclopropa [a] naphthalene is accessible via reduction of 1,1-dichloro-1H-cyclopropa [a] naphthalene with LiAlH 4 /AlCl 3 . Several derivatives of tetrahydrocyclopropa [a] naphthalene were synthesized. However, contrary to their 1,1-dihalogeno analogues, they afforded no cycloproparenes upon attempted aromatization

Oxidation of sulfides with PhIO/RuCl2 (PPh3)3 leads to sulfones. Electronwithdrawing substituents in the aromatic ring of PhIO reduce the reactivity and improves selectivity of the system. Thus, with m-iodosylbenzoic acid sulfides are converted to sulfoxide. Under the same conditions aliphatic primary alcohols are transformed to aldehydes with m-iodosylbenzoic acid, while PhIO affords carboxylic acids.

Dehydrogenation of hydroaromatic compounds with quinones was reinvestigated in the light of recent criticism of the reaction mechanism. Kinetic and spectroscopic evidence shows that disappearance of substrate proceeds at the same rate as the product-forming step. A mechanism consisting in fast formation followed by slow decomposition of an intermediate can be ruled out. The order of reactivities of 1,4-cyclohexadiene (1), 1,4-dihydronaphthalene (8) and 9,10-dihydroanthracene (11) changes in going from benzoquinone to chloranil or 2,3-dichloro-5,6-dicyanobenzoquinone. It is suggested that this behaviour could be due to contribution of CT-complexes or HOMO-LUMO interactions for determining the reactivity of the substrates.

Sodium cyanide in hexamethylphosphoric triamide selectively cleaves methyl esters in the presence of ethyl esters with yields of ca. 80%. The mechanism of the reaction has been investigated. It consists of nucleophilic displacement by cyanide of the carboxylate ion from the alcohol carbon atom (BAl2 mechanism).

Reaction of 1, 1-dichloro-2, 5-diphenylbenzocyclopropene (10a) with 1 equiv. of silver fluoride yields 1-chloro-1-fluoro-2, 5-diphenylbenzocyclopropene (10c). Both 10a and 10c react with excess silver fluoride to give the difluoro compound 10b. Both 10b and 10c are also prepared via cyclo-additions of 1, 2-dichloro-3, 3-difluorocyclopropene (14) or 1, 2, 3-flurocyclopropene (13) with diphenylbutadiene and subsequent aromatization with base. Similarly. 1-chloro-1-fluorobenzocyclopropene (16) is accessible from butadiene and 13.

cis- and trans-(3,6-D2)-1,4-cyclohexadienes 1a and 1b have been synthesized from cis-3,4-dichlorocyclobutene (5). Aromatization to benzene with DDQ is cis-stereospecific with an uncertainty of 5%. This result is discussed in relation to concerted or stepwise mechanisms for aromatization of 1,4-dihydroaromatics with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ).

The C,C-bond cleavage which occurs during chromic acid oxidation of t-butylphenylmethanol (1) and 1,2-diphenylethanol (2) to the extent of up to 67% is reduced to 3% for 1 and 13% for 2 when the reaction is run in acetone, and totally suppressed upon co-oxidation of the alcohols 1 and 2 with oxalic acid. Similarly, the yield of 7-norbornanone obtained from 7-norbornanol (7) is raised in going from acetic acid (24%) to acetone (41%) and approaches 100% in the co-oxidation. With the co-oxidation 5-endo-bicyclo [2.1.1]hexanol (3) is converted to the corresponding ketone in 54% yield. Mechanistic implications of these results are discussed.

1H-Cyclopropa[b]naphthalene 3c and the 2,7-diphenyl-substituted derivative 3a have been synthesized via cycloaddition of the appropriate isobenzofurans 1a and 1b to 1-bromo-2-chlorocyclopropene and aromatization of the adducts with low-valent Ti. The same procedure afforded the 2,7-dimethyl-H-cyelopropa[g]isoquinoline (15), but failed for the parent azacompound. Reaction of adducts of furans to 1-bromo-2-chlorocyclopropenes with low-valent Ti produced mixtures of cyclopropabenzenes 19 and 1,6-dihalogeno-1,3,5-cycloheptatrienes 18. The latter could be converted to cyclopropabenzenes with BuLi.

1H-Cyclopropa[b]naphthalene (10a) and 3-methyl or dimethyl derivatives have been synthesized by interception of appropriately substituted o-quinodimethanes 3 with 1-bromo-2-chlorocyclopropene 5, and subsequent dehydrohalogenation of the adducts. The o-quinodimethane derivatives 3 in turn were obtained from the diynes 7via base-induced isomerization to bisallenes 8 and thermal electrocyclic ring closure.

Equilibrium constants for oxidations of cyclanols by cyclohexanone in benzene have been determined in the presence of aluminium isopropoxide. The free energies of the equilibrium (ΔGox) are correlated with equilibrium constants for dissociation of cyanohydrins, rate constants for cyclanol oxidation with chromic acid, ketone reduction with sodium borohydride and trifluoroethanolysis of tosylates.

The steric requirements of leaving groups for 14 bridgehead derivatives have been examined using MM2 calculations. The strain varies almost monotonously throughout the series upon variation of the leaving group from H to C1, OH, CH3, CH3CH2O, (CH3)3CO, (CH3)3C and no significant trends for differential F-strain effects are detected expect for the perhydrophenalene derivative 13. The experimental rates of solvolysis of bridgehead derivatives correlate well with the calculated steric energy differences between substrate R-X and the corresponding carbenium ion R. However, the strain calculations using the more recent force-fields (MM2) disagree, in part, with those reported in the literature: chloride and p-toluenesulfonate leaving groups correlate with identical slopes, and the perhydrotriquinacene derivative 10 shows no anomalous behavior. The calculations suggest that F-strain and C,C-hyperconjugation should not play any dominant role in bridgehead solvolysis.

Base-induced elimination of the sulfonium salt 2i in the presence of furan affords the addition products 7 and 8, derived from 1H-cyclopropa[l]phenanthrene (1) and the isomeric cyclopropene 5a(Scheme 3). Upon oxidation, the selenide 2c yields phenanthrene-9-methanol (9), presumably via1. No evidence for the intermediate 1 is obtained from sulfoxide pyrolysis with 2e, which leads to products formed by radical pathways (Scheme 5). Reductive elimination of the disulfone 3b gives half-reduction to monosulfone 2g and complete reduction to cyclopropane 2 as well as 9-methylphenanthrene (15), but no evidence for the intermediate 1.

The activation parameters for the oxidation of 13 secondary alcohols with chromic acid have been determined. Application of a statistical treatment of Exner [9] shows that the reactions are isoentropic with an average entropy of activation (ΔS≠) of −24.0 e. u.

The rates of oxidation with chromic acid of 15 bi- and polycyclic secondary alcohols have been measured and correlated with strain changes calculated by the MM1-program between the alcohols and the corresponding ketones. A correlation of the same quality is obtained upon representation of OH-strain by CH3-strain. The significance of the correlations with respect to the oxidation mechanism as well as the limitations of the applicability of force-field calculations to reactivity problems are discussed.

1, 1-Difluorocyclopropa[a]naphthalene (1b) is prepared in three steps from 4-bromo-1,2-dihydronaphthalene (7) via carbene addition, benzylic bromination and bidehydrohalogenation. Structural evidence for formation of 1b is based on 1H- and 19F-NMR spectroscopy. Compound 1b is stable in solution at −30°. Upon reaction with MeOH/H+ it is converted to a 1:2 mixture of 1- and 2-methylnaphthoate (10 and 11, respectively).

The linear free energy relationship of Sicher for relative reactivity towards chromic acid oxidation (ΔΔG) as a function of thermodynamic stability (ΔG) has been reexamined with 23 pairs of epimeric alcohols. The plot of ΔGvs. ΔG has a slope of 0.8, a correlation coefficient of 0.97 and a standard deviation of 0.23 kcal/mol on ΔΔGOx. The limitations of the relationship and the exceptions are discussed.

The title compound 1 was synthesized via addition of dichlorocarbene to dimethyl trars-3-hexenedioate (5), using o-nitrophenylselenic acid-elimination to form the double bonds. Reaction of dichlorocyclopropane 8 with ozone on silica gel furnished the monoketone 10; no diketone 11 could be isolated upon further exposure of 10 to O3/SiO2. When the bis(p-toluenesulfonate) 13b was treated with t-BuOK, 16 was obtained in low yield as the only isolable product. It is believed to arise from Cope-rearrangement of an intermediate cis-divinylcyclopropane 14 to cycloheptadiene 15, which undergoes a subsequent allylic rearrangement to 16.

Molecular-mechanics calculations for strain of carbenium ions are tested using Bentley's unified reactivity scale for bridgehead solvolysis as reference. Excellent correlations are obtained for solvolytic bridgehead reactivity with the calculated steric-energy difference (?Est) between substrate (R--H or R--OH) and cation (R+). After adjustment of appropriate force-field parameters, the approach is successfully extended to the rigid, but planar cations derived from structures 15-20; however, the general set of parameters cannot be applied to highly strained systems such as the cation formed from 17. With all of the 18 sets of parameters tested, the 2-endo-norbornyl derivative 16, is adequately correlated, while the exo isomer 15 exhibits enhanced reactivity by a factor of ca. 102 to 103.

The rates for the reduction of ketones with sodium borohydride are interpreted in terms of two parameters, both derived from force-field calculations; i.e. the strain difference between alcohol and ketone (Δ strain) and the steric hindrance towards approach of the hydride R. Models for the evaluation of R are discussed. With this approach reduction rates over a range of 108 can be rationalized within a factor of 6–10.

Sodiumthiophenoxide and sodiumphenylselenide react with N-benzyl- and N-hexyl-di-p-toluenesulfonamides (1 and 2) via displacement at the C-atom to afford the corresponding organosulfides and selenides in yields of 68–96%. In contrast, sodium cyanide converts disulfonamides to monosulfonamides by attack on the S-atom. The different selectivities of phenylsulfide and selenide as compared to cyanide anions with respect to attack on the C- and S-atoms are rationalized on the grounds of the HSAB (hard and soft acids and bases) principle of Pearson.

The stereochemistry of the Diels-Alder reaction of 1,2-dichloro-3,3-difluorocyclopropene (5a) to 1,4-diphenyl-1,3-butadiene (6) and 1,3-diphenylisobenzofuran (7) was unambiguously established by X-ray structure determination. In all cases known so far, tetrahalogenocyclopropenes add exo to open-chain dienes and furans. The previously reported exo-addition product (2a) of l-bromo-2-chlorocyclopropene (5b) to 7 allows assignments of the stereochemistry of other additions of 5b to furans. exo-Addition usually predominates, but in some cases endo- adducts are also formed. This contrasts with reports in the literature that 5b adds preferentially endo to open-chain dienes.

A series of 3,4-disubstituted (4a, b) or 3,4-fused (4c-e) 1,1-di-fluorocyclopropabenzenes, including the very strained 1,1-difluoro-3,4-dihydro-1 H-cyclobuta[a]cyclopropa[d]benzene (4e) have been synthesized and characterized. Dissolution of these difluoro derivatives in fluorosulfonic acid affords the fluoro cations 3a–e. 1H-, 19F-, and 13C-NMR data of the cations are reported and discussed with respect to those of the precursors.